Vinyl acetate is commonly produced by the reaction of ethylene, oxygen and acetic acid in the presence of a palladium-gold catalyst. See, for example, U.S. Pat. No. 3,743,607. Palladium and gold are expensive precious metals. Therefore, many efforts have been made to increase the catalytic activity and reduce the amount of catalyst needed. For example, U.S. Pat. No. 6,022,823 teaches calcining the support impregnated with palladium and gold salts prior to reducing the metals. The catalyst shows improved activity.
The acetoxylation of ethylene to vinyl acetate is commonly performed in a gas phase, fixed bed tubular reactor. Vinyl acetate is recovered by condensation and scrubbing, and purified by distillation. Unreacted ethylene, oxygen and acetic acid are recovered by distillation and recycled to the acetoxylation. In addition to vinyl acetate, the acetoxylation produces a number of byproducts, including carbon dioxide, water, and ethylene glycol diacetate. Carbon dioxide is primarily produced by the combustion of ethylene and vinyl acetate. Carbon dioxide is removed from the reaction product mixture by distillation and absorption with a potassium carbonate solution.
U.S. Pat. No. 6,420,595 discloses a method of real time process control in a reaction system for the production of vinyl acetate from the oxidation of ethylene and acetic acid. Reaction system samples are collected from the reactor vessel feed and/or effluent and/or from columns and/or transfer lines downstream of the reactor vessel, and the concentration of one or more components in the sample is measured by an infrared analyzer. The concentration measurements are then used to make adjustments in the concentration of components in the reaction system, directly or directly or indirectly, such as by adjusting the temperature profile in a particular column, the flow rate of solution into or out of a column, or the addition or extraction of a component to or from the solution. For optimum process control, the measurements are transmitted to a control unit for real time analysis, and the adjustments are made almost instantly after the infrared analysis.
One issue associated with the use of infrared analysis in the mid infrared range of 400 to 4000 wavenumbers (cm−1) to control a vinyl acetate production process is that the infrared signal cannot be transferred by optical fiber over long distance so that the measurement can be readily integrated into the control system. New methods for controlling the vinyl acetate production process are thus needed. Ideally, the method can directly measure the concentrations of multiple components of the vinyl acetate production process and the measured results can be directly transferred to the control room to control the production process.